HUANCAVELICA, Peru – Sonia Salazar’s house, like most in her neighborhood, is built of adobe bricks made from mud that soaked up centuries of emissions from mercury smelters.

Now scientists are trying to determine whether those houses – in the shadow of a hill that once held the hemisphere’s largest mercury mine – pose a health hazard to their inhabitants.

In the 16th and 17th centuries, mercury furnaces blasted day and night around this town high in the Andes Mountains. Eventually the town expanded over smelter sites and waste piles.

The researchers already have found high levels of mercury contaminating the soil as well as adobe walls, dirt floors and the air inside some houses. They are now analyzing people’s hair to measure their mercury exposure.

Salazar, who is raising her four children in one of those houses, is among the residents waiting to hear whether they are being poisoned by their own houses.

“It’s worrisome,” Salazar said. “It’s like an illness that gets into children.”

Huancavelicans call their town the tierra del mercurio – the land of mercury – and even the mayor recalls having played, as a boy, with little silver balls that oozed out of the sides of ditches or building foundations.

The capital of a region with some of Peru’s highest poverty, malnutrition, and infant mortality rates, Huancavelica grew up around a plaza still flanked by colonial buildings. Residential neighborhoods gradually spread along the river and up the hillsides.

“Eighty percent of the houses are made of adobe. Those are the people who have the fewest resources,” said Rubén Espinoza, an archaeologist and anthropologist working with the mercury study team.

The study, which combines historical detective work with scientific analysis, might never have happened had it not been for the bizarre behavior of a priest.

Historian Nicholas Robins, director of the non-profit Environmental Health Council and a teaching assistant professor at North Carolina State University, was researching an 18th century Indian rebellion in Peru when he stumbled across a colorful description of Juan Antonio de los Santos. The priest’s erratic behavior and violent outbursts terrified parishioners and led a colonial government official to suggest that his superiors commit him to an insane asylum.

The priest had spent years in Potosí, Bolivia, at the foot of Cerro Rico, the “rich hill” that for centuries supplied the silver that fueled global trade. Like small-scale miners today, colonial miners used mercury to extract silver from ore, sending tons of toxic vapor wafting over the city.

Robins wondered if the colonial cleric might have been suffering from mercury poisoning. The question led him to examine historical records of the amount of silver produced in Potosí and the mercury used to extract it.

Robins estimates that miners in the Bolivian town used some 39,000 metric tons of mercury to produce silver between 1574 and 1810. Much of that mercury came from Santa Barbara Hill, which looms over Huancavelica, about 12,000 feet above sea level. The main mine portal, now sealed, still sports a colonial arch and Spanish coat of arms.

The Spaniards’ forced-labor system sent tens of thousands of Andean Indians into Santa Barbara’s labyrinth of tunnels to dig cinnabar ore. So many workers perished that Santa Barbara became known as “the mine of death.”

When cinnabar ore is heated, the mercury that vaporizes can be condensed, captured and stored as a liquid. Based on colonial records, Robins calculates that miners in Huancavelica produced about 68,200 metric tons of mercury in the 16th and 17th centuries, and about one-fourth of that was released into the atmosphere from smelters.

“I think it is impossible to dump 17,000 metric tons plus of mercury in a community or release it into the air and not have significant consequences,” he said.

To investigate those consequences, Robins enlisted Nicole Hagan, who is now a doctoral candidate in environmental science and engineering at the University of North Carolina.

In 2009, using historical records, Robins and Hagan mapped the main colonial-era smelting zones in Potosí and Huancavelica, then modeled airflow patterns. Based on those results, they laid out transects and took soil samples.

High mercury concentrations were found in soil samples from both towns, although they were higher in Huancavelica, where the cinnabar ore was smelted.

Hagan said the soil levels are consistent with measurements near mercury mines in other parts of the world. The difference, however, is that over the years, many Huancavelica residents have constructed their homes from adobe bricks made with the contaminated soil.

In about 20 percent of 60 houses tested by the scientists, the indoor air concentration of mercury is between 1 and 10 micrograms per cubic meter, which exceeds levels considered safe under U.S. guidelines.

In addition, about three-quarters of the dirt floor and adobe brick samples taken inside the homes were higher than the Environmental Protection Agency’s screening level for mercury in soil. Many houses, like Salazar’s, have dirt floors where children play.

For Robins and Hagan, the next question is whether the contaminated building materials are affecting residents’ health. “It is not clear how volatile or bioavailable the mercury from historical depositions is and to what extent the mercury presents a health hazard,” Hagan said. “All forms of mercury are toxic, but the species of mercury and the exposure route will determine the extent of the toxicity.”

Methylmercury affects the neurological system, especially in children, and it has been linked to IQ reductions of children exposed in the womb. High levels can affect the kidneys and brain, causing tremors, irritability, and vision, hearing and memory problems.

Despite the long history of mercury pollution in Huancavelica, no health studies have ever been done there, according to Enrique Ecos, who heads the local hospital’s epidemiology department and collaborates with Robins and Hagan.

Government officials say they are busy trying to address the town’s urgent concerns like potable water and sanitation.

Last July, the team returned to Huancavelica to inform the residents of their results to date. They also took more than 100 hair samples from adults living in many of the homes they sampled in 2010, and also from people in brick houses with concrete floors, where mercury exposure is likely to be lower. They are awaiting the results.

Hair samples might not be conclusive about the risks posed by the homes because they could be contaminated with other airborne mercury, according to Philippe Grandjean, adjunct professor of environmental health at the Harvard School of Public Health, who recommended measuring mercury in urine. Nevertheless, Grandjean said, Robins’ and Hagan’s findings point to the need for further study.

Their main goal is to assess possible health impacts and recommend measures for reducing exposure. That could mean finding an effective, low-cost, culturally acceptable way to seal or shield the adobe bricks, Hagan said. A brick-making cooperative using uncontaminated clay is another option, Robins said. Soil cleanup, if necessary, could be costly, but might create jobs while improving public health.

Robins, whose book, Mercury, Mining and Empire: The Human and Ecological Cost of Colonial Silver Mining in the Andes, was published in 2011, hopes to expand health studies and community outreach while working on ways to protect people.

He is fond of quoting a Spanish governor of Peru who once said, “In Huancavelica, there is much to be remedied.” The governor was referring to government corruption, but Robins said he just as easily could have been talking about its environment.

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.